Conventionally, inorganic photoconductive substances such as selenium, zinc oxide, cadmium sulfide and silicon have widely been used in an electrophotographic photosensitive body. Those inorganic substances had many advantages, and simultaneously had various disadvantages. For example, selenium has the disadvantages that its production conditions are difficult and it is liable to crystallize by heat or mechanical shock. Zinc oxide and cadmium sulfide have problems in moisture resistance and mechanical strength, and have the disadvantage such that electrostatic charge and exposure deterioration take place by a coloring matter added as a sensitizer, thus lacking in durability. Silicon involves that its production conditions are difficult, cost is expensive because of using a gas having strong irritating properties, and care should be taken to handling because of being sensitive to humidity. Additionally, selenium and cadmium sulfide have the problem in toxicity.
Organic photosensitive bodies using various organic compounds that improved disadvantages of those inorganic photosensitive bodies are widely used Organic photosensitive bodies include a single layer photosensitive body having a charge generating agent and a charge transport agent dispersed in a binder resin, and a multi-layered photosensitive body having a charge generating layer and a charge transport layer functionally separated. The characteristics of such a photosensitive body called a functional separation type are that a material suitable to the respective function can be selected from a wide range, and a photosensitive body having an optional function can easily be produced. From such a situation, many investigations have been carried out.
However, although organic materials have many advantages that are not possessed by inorganic materials it is the present situation that organic materials sufficiently satisfying all of characteristics required in electrophotographic photosensitive bodies are not obtained. That is, a decrease in charged potential, an increase in residual potential change in sensitivity and the like due to repeated use give rise to deterioration of image quality. Cause of this deterioration is not completely clarified, but active gases such as ozone and NOx generated when charging due to corona discharge decomposition of a charge transport agent or the like by ultraviolet light and heat contained in light for exposure and light for removal of electricity, and the like are considered as some factors. For suppression of those deteriorations, a method of combining a hydrazone compound and an antioxidant (for example, see Patent Document 1), a method of combining a butadiene compound and an antioxidant (for example, see Patent Document 2), and the like are known. However, organic materials having good initial sensitivity are not sufficiently improved in deterioration due to repeated use, and organic materials having less deterioration due to repeated use have the problems in initial sensitivity and charging properties Thus it is the present situation that the effect for suppressing deterioration is not yet sufficiently obtained.
Patent Document 1: JP-A-1-44946
Patent Document 2: JP-A-1-18845